The present invention relates to an elevator valve apparatus for controlling a hydraulic actuator for driving an elevator cage of a hydraulic elevator.
In general, the elevator cage of the hydraulic elevator is driven to ascend and descend by a hydraulic cylinder through or without through pulleys. In order to drive to ascend and descend the elevator cage with a predetermined speed characteristic, it is necessary to control supply flow of hydraulic oil supplied from a hydraulic pump to the hydraulic cylinder and discharge flow from the hydraulic cylinder to an oil tank with a predetermined characteristic.
Generally, by means of controlling bleed-off flow bleeded off from discharge flow of a fixed discharge hydraulic pump, the supply flow is controlled indirectly.
In the elevator valve apparatus, there are provided with a solenoid proportional control valve means for ascending which controls the bleed-off flow, and a solenoid proportional control valve means for descending which controls the discharge flow from the hydraulic cylinder.
In one system called a pilot system, each of above control valve means is comprising a pilot solenoid proportional control valve and a flow control valve which is operated by the pilot pressure generated with the pilot control valve.
In other system called a direct drive system, each of above control valve means is comprising a solenoid flow control valve.
Furthermore, the elevator valve apparatus is provided with a control means for controlling above two control valve means. As the control means, two systems have been known. One controls the control valve means by open loop control according to a predetermined characteristic and the other controls the control valve means by feedback control in accordance with a predetermined characteristic and actual supply flow and discharge flow which are detected by a flow detecting means.
For example, in No. 84 (1986), vol. 21 of [Elevator Kai] issued by Nippon Elevator Association, described is an elevator valve apparatus comprising a control valve means of the direct drive system and a control means of the feedback control system. In addition, in Japanese Patent Publication No. 62-25881, disclosed is a hydraulic control apparatus similar to that of above apparatus.
Generally, the cage of the hydraulic elevator is driven to ascend and descend with a given velocity characteristic including acceleration, high speed movement, deceleration, low speed movement and rapid deceleration for stopping, in each of ascending and descending.
In the prior elevator valve apparatus, the velocity characteristic is an approximately trapezoidal characteristic in which the velocity in acceleration and deceleration varies linearly, and therefore the magnitude of accelerating and decelerating rate is rather large in starting of acceleration and deceleration and also in stopping of acceleration and deceleration, and therefore this reduces the comfortability in riding for the passengers.
Furthermore, in the case where the loading pressure dependent on the loading weight fluctuates largely, the hydraulic pressure in the cylinder fluctuates rapidly in starting of ascending to induce an oscillation with shock on the cage or to cause a delay in starting of ascending.
In the control means of the feedback control system, there are some disadvantages such that a flow detecting means of large capacity has to be provided, the initial adjustment of the feedback control system is very troublesome, hunting is caused easily when the control system is unstable, and so on.
On the other hand, in the control means of the open loop control system, there is a disadvantage such that it is difficult to control ascending or descending of the cage with a predetermined characteristic, since the supply flow and the discharge flow fluctuate when the discharge flow of the pump and the passing flow through the control valve means fluctuate due to the fluctuations in the loading pressure in the hydraulic cylinder corresponding to the oil temperature and the loading weight in the cage.
Furthermore, during operating for long period after the installation of the hydraulic elevator, the volumetric efficiency of the hydraulic pump decreases due to the increase of the interior leakage flow, then the discharge flow from the pump decreases gradually. That is, when the discharge flow of the hydraulic pump decreases, the ascending acceleration performance deteriorates, and the ascending maximum speed decreases, ascending low speed after deceleration and before stopping decreases. The deterioration of the acceleration performance and the decrease in the ascending maximum speed do not cause vital problems. However, when the ascending low speed decreases, the stopping position of the cage fluctuates, since a rapid deceleration for stopping is done is a constant minute time, and the cage stops at a level lower than the floor level where the cage should stop. Thus, the stopping positional accuracy decreases remarkably, and this is a vital problem for the elevator.
The same problem also occures in the case where the supply flow fluctuates due to fluctuations of the oil temperature or the loading hydraulic pressure in the cylinder.